If you are an American, using quotation marks could hardly be simpler: Use double quotation marks at all times unless quoting something within a quotation, when you use single. It’s different in the greater Anglosphere, where they generally use singles in books and doubles in newspapers. It’s still pretty simple, but nothing so straightforward as here.
Yet some of us don’t seem happy with what we’ve got. For several years now in teaching writing classes to college freshmen, I’ve noticed some students adopt another rule: double quotes for long quotations, single quotes for single words or short phrases. They’ll quote a long passage from Measure for Measure accurately, but when they want to quote one of Shakespeare’s words, a cliché, or some dubious concept like “virtue,” they’ll go with single quotes.
It took me a while to understand what was going on, but after thoroughly studying it I developed a rigorous explanation for this staggering decline in standards: kids today.
But then I looked up from their papers to find this usage in the manuscript of a friend’s novel. Then I saw them in another friend’s manuscript—this time, of an academic book. Then I turned to the Internet and they were everywhere—in a local news story, in a paper by a college professor, in a blog on social marketing, in a blog on the education system, on the website of the Children’s Literacy Foundation. In each case, the same short/single, long/double quote rule was followed.